PROJECT ABSTRACT/SUMMARY Approximately 15% of children under 5 have obesity. Research shows that parents are the primary influence on young children?s weight-related behaviors and resulting weight status. However, research in this area has focused almost exclusively on mothers; less than 10% of studies on parenting and childhood obesity published since 2009 include any results for fathers. Overlooking fathers in childhood obesity research is concerning given emerging research identifying the strong influence of fathers on children?s weight outcomes. Guided by the Lifecourse Theory and leveraging a unique opportunity in a large, national study (the Growing Up Today Study, GUTS), we will develop a large cohort of fathers and examine: (1) preconception and contemporary factors influencing fathers? weight-related parenting; (2) developmental pathways linking fathers? preconception behaviors, weight-related parenting and children?s weight outcomes and behaviors, and (3) how fathers? parenting compares and interacts with that of mothers. To address these aims, we will use utilize existing measures of fathers? weight-related behaviors collected since adolescence and compile new data on their parenting engagement and their food, physical activity, media and sleep parenting practices. This study?s large (n=1000) and diverse sample of fathers ? including biological, adoptive and social fathers ? provides an unparalleled, time-sensitive opportunity to examine the influence of fathers on their young children?s weight-related behaviors and outcomes. Results from this study will guide the timing, intensity and content of preconception care and family-based childhood obesity prevention interventions.